Priority is claimed to Korean Patent Application No. 10-2003-0100494, filed on Dec. 30, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a polycrystalline silicon device and a thin film transistor (TFT) having the same, and more particularly, to a polycrystalline silicon device with uniform mobility and a TFT having the same.
2. Description of the Related Art
Polycrystalline silicon (poly-Si) has higher mobility and better light stability than amorphous silicon. Such poly-Si is used widely in various application fields, particularly, in TFTs or memory devices. A poly-Si TFT is used, for example, as a switching device of a display. Examples of a display device using an active element such as a TFT include a TFT-liquid crystal display (LCD), a TFT-organic light emitting diode (OLED), or the like.
The TFT-LCD or the TFT-OLED has a structure in which a TFT is disposed on each pixel among pixels arranged on an X-Y matrix. The performance of an LCD, an OLED, or the like in which a plurality of TFTs are arranged greatly depends on the electric characteristics of the TFTs. One of major characteristics a TFT requires is higher mobility of a Si active layer. Crystallization is necessary for increasing the mobility of the Si active layer. The development of poly-Si approaching single crystalline is one of the important study tasks to crystalline silicon. U.S. Pat. No. 6,322,625 discloses a method of manufacturing high-quality silicon crystalline. Many studies on the crystallization of silicon have contributed to obtaining a crystalline structure approaching single crystalline.
However, the improvement of the uniformity of polycrystalline is a problem to be still solved and a subject to be presently studied. For example, in a case of the TFT-OLED, desired mobility is 5 to 30 cm2/Vs, which is satisfied with a technique for manufacturing poly-Si capable of realizing the mobility of about 100 cm2/Vs.
However, the uniformity of mobility is less than several percentages, while according to the results of present studies, the mobility is about 80 to 20 cm2Ns, and thus the mobility deviation is about 20%. The mobility deviation of this degree deteriorates the quality of a display device.